1. Field of the Invention
The present invention relates to a spot welding tip detaching apparatus which detaches a tip being an electrode fitted in a spot welding gun.
2. Description of the Related Art
In a production line of automobile bodies, spot welding is often used. The spot welding is a welding method in which metal plate materials or the like which are laid one on the other are sandwiched from both sides and by the local application of pressure and the passage of an electric current, metals are melted by resistance heat to make the metal plate materials adhere to each other.
In the spot welding, an apparatus called a spot welding gun (hereinafter, a welding gun) is generally used. The welding gun welds metal plate materials or the like by sandwiching the metal plate materials by a pair of electrodes and passing an electric current therethrough while pressing them. The electrodes are fitted in tip portions of bar-shaped members (hereinafter, shanks), one of the tip portions facing the other tip portion. One of the shanks or both of them is (are) capable of advancing/retracting, which enables the electrodes to sandwich the metal plate materials or the like.
The electrodes of the welding gun are generally called cap tips (hereinafter, tips). The tips are deformed or worn away due to long-time use, and such deformation or wearing, if any, sometimes makes it impossible to maintain desired welding quality. Therefore, in the welding gun, the tips are periodically replaced.
As an apparatus for tip replacement, an apparatus is on the market which detaches a tip by moving a welding gun, inserting the tip to a holder part of a tip detaching apparatus, and after holding the tip by a chuck device, such as an air-operated chuck, moving the welding gun in an up and down direction while rotating the tip by an electric motor or the like.
Further, Japanese Laid-open Patent Publication No. 2006-346701 and Japanese Laid-open Patent Publication No. 07-144284 disclose methods for detaching a tip by inserting a plate-shaped member into a gap between the tip and a shank on a tip mounting side and prying the tip and the shank by a robot operation or device.
However, the aforesaid apparatus on the market requires the air and electric motive power used for holding the tip and for detaching the tip and thus has problems that it has a complicated structure and high cost.
Further, the apparatuses disclosed in Japanese Laid-open Patent Publication No. 2006-346701 and Japanese Laid-open Patent Publication No. 07-144284 require a certain size of gap between the tip and the shank. Therefore, a gap large enough to enable the detaching of the tip cannot be sometimes reserved depending on a state of the gap and the shape and size of the welding gun, that is, the type of the shank (tip base) and the size of the tip (for example, φ16 or φ13), which has posed a problem that these apparatuses cannot be flexibly used. Further, since the tip is pried when detached, the shank, for example, is sometimes damaged, which sometimes necessitates the replacement of the shank and so on because the shank and so on are deformed after the long use.